Popularity of wireless communication devices, particularly mobile stations is still growing rapidly. Owing to this, the capacity of present mobile station networks is occasionally almost fully occupied, wherein situations may occur, when the data transmission connection cannot be formed at the very moment when the user wishes. The capacity of existing mobile communication systems cannot always be increased, but for serving additional users new mobile station networks are built. In such new mobile station networks, the geographical coverage is not necessarily very wide at the initial phase and, consequently, it is useful if the user is able to choose a network whose coverage area he or she is located in at the time. For this purpose so-called multi-mode phones have been developed, these being connectable to two or even more various mobile station networks.
Mobile stations are used also for transmitting other information than speech. Many users have also a portable laptop PC at their disposal, wherein they have a possibility to send and receive e.g. facsimile copies, e-mail, files or even video image by using a mobile station network. Further, the use of Internet network on the move is increasing e.g. because of the fact that via Internet network one can find a myriad of information which the user needs at the time. Such system allowing the movability of the user adds to the productivity of the user e.g. by increasing the efficiency of data acquisition and data transmission.
Increasing use of mobile station networks has accelerated design of new, more efficient mobile station networks. However, the design has not lead into one common standard, instead various mobile station standards have been developed, wherein it is very difficult, if not even impossible, to implement mobile stations by using prior art solutions in a manner that the implementation of the mobile station covers all possible mobile station networks. On the one hand, there exists a need to manufacture mobile stations which can be connected to more than one mobile station network, e.g. as a result of said increased mobility of users. On the other hand, manufacturing costs of a mobile station should be kept at a reasonable level, e.g. because of the fact that increasing competition on the mobile station markets decreases selling prices, which for its part limits the quantity of properties implemented in one mobile station.
Mobile stations that can be connected to various mobile station networks comprise e.g. separate radio parts for each mobile station network. However, a part of the functions, such as the display, keypad, microphone and earpiece are common for all the modes. One drawback of such mobile stations is that it has so far been impossible to manufacture them in small size, and furthermore, their manufacturing costs are relatively high. A further disadvantage that can be mentioned is the fact that such mobile stations only operate in those mobile station networks which have been selected by providing at the manufacturing phase the mobile stations with functions corresponding to these networks. However, the user may change his or her location to areas where no system defined in the mobile station is available, but where possibly some other system is used. Thus, the use of such mobile stations is not very flexible, particularly in situations where the type of mobile station network which can be used in said location is not known in advance. The user should thus have several different mobile stations in order to ensure that connecting is successful.
Finnish patent FI-89434 of the applicant describes a radio telephone assembled of separate modules and comprising a basic module and at least one additional module which can be coupled thereto in a detachable manner. The radio telephone described in the patent publication is regarded as being connectable either to an analog or digital mobile station network, according to what is needed, wherein the basic module comprises such parts and functions that are common to telephones operating both in analog and digital modes. The additional module coupled to the basic module includes at least the main part of the electrical circuits required for sending and receiving an analog signal, wherein when it is coupled to the basic module, the telephone operates as an analog telephone. On the other hand, it is possible to couple to the basic module an additional module which includes at least a main part of the electrical circuits that are required for sending and receiving a digital signal, wherein when it is coupled to the basic module the telephone operates as a digital telephone.
Finnish patent application FI-952814 of the applicant describes another solution for forming a data transmission connection with two or more different mobile station networks. A telecommunication terminal described in the publication comprises means for forming a connection to different mobile station networks, wherein the telecommunication terminal examines, when the connection is formed, which mobile station networks are available in the area in question, and selects one of these mobile station networks and sets the operating mode of the telecommunication terminal to correspond to the selected mobile station network. To a this type of mobile station network or to a coupling unit connected thereto an additional unit has been mounted in advance for each mobile station network that is arranged to be selected.
In practice, the implementation of mobile stations involves several drawbacks restricting the quantity of properties that can be added to one mobile station. In particular manufacturing costs and the small size of the devices are such restricting factors, wherein in practical mobile stations it is possible to implement at the most two or three different systems or protocols. However, since there exists a much larger number of different mobile station networks, analog and several digital systems, the number of different system combinations is very large, which by using prior art techniques means that it is not sensible to implement all the possible combinations in mobile stations.
In accordance with functions, mobile stations can be mainly divided into to separate parts:
A basic part comprising those functional portions which can be used in mobile stations according to different mobile communication systems, and a control unit. This part typically comprises processing portions of signal, e.g. processing means, memory means, keypad, earpiece, display and microphone. PA1 A particular part whose properties depend on the system, standard and protocol. Thus, in this part those special features are implemented which cannot be implemented collectively for the different systems. In practise, this part can be further divided into software and equipment parts. The software part comprises the system specific software which, together with the basic part and the system dependent part, implement functions of a certain protocol or system. The equipment part typically comprises the data transmission devices used at the time in wireless communication devices, e.g. a radio part or an infrared sender/receiver. In other words, the system specific equipment part enables a wireless data transmission between a terminal equipment (TE) and an access point (AP) of the system in accordance with the system specifications.